test(push): pin preflight label + time-series validators

[LukasWodka]

Summary

Second follow-up from the mutation-testing pass — the preflight.go cluster (the biggest, 35 survivors). These are the ingestion-correctness gates, so an unguarded boundary here silently lets a bad dataset through local pre-flight. This PR takes the pure / in-memory-testable validators (no fixtures) and kills their survivors:

Validator	Mutant killed	Test pins
CheckLabelColumn	matchColumnIndex(...) >= 0 → > 0	a label column in the first header slot (index 0) is still accepted
CheckAnnotationPairing	len(noAnn) > 0 / len(noImg) > 0 → >= 0	an asymmetric mismatch reports only the orphaned side (no bogus "0 X ()")
labelConstantViolation	len(shown) > 5 → >= 5	constant-label-per-sequence + the "+N more" truncation (exactly 5 → no (+N more))
perGroupTimeViolation	both len > 5 truncations	numeric-time ordering + invalid-value and out-of-order truncation boundaries
isNumericTimeColumn	switch-selector	numeric (INT/FLOAT/DECIMAL/…) vs temporal branch

Mutation-proven: 3 representative mutants (the matchColumnIndex boundary, a len > 5 truncation, a len > 0 clause) were flipped in-source and confirmed to fail the matching test; the parallel truncation/asymmetric cases share the same operator.

Deliberately not chased: the isNumericTimeColumnIndexByte guards (equivalent — post-TrimSpace, index-0 is impossible). The fixture-needing validators (ValidateImages, CheckCSVEncoding, scanTSCRows, CrossCheckLabels, HasBOM) are a natural follow-up.

Test plan

• make ci green (build, vet, gofmt -s, go test -race, errcheck/ineffassign/misspell, schema-check). Pure additive test file; no production change.

🤖 Generated with Claude Code

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Note

Low Risk
Test-only additive change; strengthens guards on ingestion preflight behavior with no runtime impact.

Overview
Adds internal/push/preflight_validators_test.go, a pure in-memory test suite that locks down edge cases in push preflight validators (no production code changes).

Coverage targets gremlins survivors: CheckLabelColumn accepts a label in the first header column (index 0); CheckAnnotationPairing reports only the orphaned side on asymmetric image/annotation mismatches; labelConstantViolation and perGroupTimeViolation enforce constant labels per sequence, numeric time ordering, and the exactly 5 vs 6"(+N more)" error truncation boundaries; isNumericTimeColumn distinguishes numeric SQL types from temporal/text and missing columns.

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[LukasWodka]

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[saadqbal]

LGTM 👍 Solid mutation-kill coverage — verified the index-0 CheckLabelColumn boundary (>=0 not >0), the asymmetric annotation-pairing clauses, the len > 5 truncation edges (5→no '+N more', 6→'+1 more'), and the isNumericTimeColumn suffix/UNSIGNED normalization. Each case earns its place.